The present invention relates to a method for removing dust or other matter from a web, namely, a flexible support made of paper, plastic or the like. More particularly, the invention relates to a method for removing dust or the like from a web which is moving.
A variety of methods for removing dust from a running web have been proposed in the art. In one of these, termed a dry-type dust removing method, unwoven cloth or a brush held suitably is pushed against a web to remove deposits from the surface of the web. (See, for example Japanese Unexamined Published Patent Applications Nos. 136764/1986 and 27309/1987 and Japanese Patent Applications Nos. 42741/1986, 7329/1987 and 94740/1987.) In another method, a stream of air high in purity is applied at high speed to a web running over a backup roll to remove deposits from the surface of the web by passing them past a suction port. In still another method, the surface of a web is polished directly with a hard member made of diamond or sapphire. (See Japanese Unexamined Patent Applications Nos. 92130/1987, 172532/1987 and 243553/1986, and Japanese Patent Application No. 132991/1987.) Moreover, there are known wet-type dust removing methods in which a web is introduced into a cleaning solution tank where deposits are removed from the web by ultrasonic vibration, or a cleaning solution such as water or organic solvent is applied to a web and deposits together with the cleaning agent are removed from the web by doctoring. (See Japanese Unexamined Patent Applications Nos. 150571/1984, 60748/1987 and 296826/1985.)
However, the above-described conventional methods have various problems. In the method of removing dust from a web using unwoven cloth or a brush, or in a method of polishing the surface of a web with a hard member of diamond or sapphire, the physical contact forms scratches on the web and generates static electricity. In addition, in the method using unwoven cloth, fibers of the unwoven cloth may stick to the surface of the web.
The method of applying a stream of air to a web at high speed is effective in removing deposits which are relatively large in diameter (more than several tens of microns); however, it is substantially not effective in removing deposits which are small in diameter or high in adhesion.
In the wet-type dust removing methods, it is impossible to completely scrape the cleaning solution off the surface of the web, and accordingly it is necessary to provide a drying zone, with the result that the cost of equipment is increased as much, and the cleaning solution is increased in cost. Also, because of the provision of the drying zone, the distance the web travels is increased as much, as a result of which foreign matter such as dust may stick to the web. Furthermore, the cleaning solution functions as a lubricant during the doctoring, and therefore foreign matter strongly stuck to the web may not be removed.